For using a sensor to detect data that cyclically changes according to factors such as pulse and movements of a body (body movements), e.g., pulse wave and acceleration, to determine pulse count or body movement pitch based on the detected data, a method is being considered for applying frequency analysis to the data that is detected at specified time intervals and for using the analysis result. When performing frequency analysis, it is possible to digitize the detected data and to apply a fast Fourier transformation (FFT) using a device, such as a microprocessor, capable of digital computation; and therefore analysis can be performed at a high speed using a compact device having a simple configuration. The analysis result of the digital processing can be expressed as a group of discrete line spectrums shown in FIG. 15, for example. That is, if the frequency range that can be sampled (sampling frequency) is 4 Hz and if it is possible to provide a 6-bit sampling address, 64 sampling points can be obtained. Frequency analysis can then produce a frequency having a resolution of 1/16 Hz as the output value. For example, if a line spectrum having a peak at the 32nd address is obtained as the result of the analysis, the detected data has a frequency of 2 Hz. This translates into a pulse count measurement of 120 pulses/minute if the detected data is a pulse wave that changes according to the pulse.
However, if a line spectrum having a peak at the 33rd address is obtained as the result of the next measurement, the resulting, pulse count is 123.75 pulses/minute which would be 123 pulses/minute after digitization (integer conversion). In other words, the aforementioned system cannot output pulse counts between 120 and 123 pulses/minute. In this way, calculating a pulse count directly from the frequency of the line spectrum obtained through frequency analysis results in unnatural values and low precision. The aforementioned example can only provide a value based on the conversion of 1/16 Hz, which is the line spectrum interval (resolution), into a pulse count, i.e., 3.75 pulses/minute, or a value that has been turned into an integer.
In order to improve the precision of the pulse count to be output, it is necessary to improve the resolution to be obtained from frequency analysis. For example, the resolution can be improved by increasing the number of sampling points, thus extending the data fetch time which is expressed as a product of sampling frequency and sampling point count. However, such a change tends to lengthen the sampling time needed for accumulating sufficient data for allowing frequency analysis because pulse count and body movement pitch have low frequencies. Even when measuring pulse with the aforementioned condition, a long data fetch time of around 16 seconds/cycle is required. Consequently, if the number of sampling points is increased to further extend the data fetch time, the time required for updating pulse count becomes extremely long, and as a result the pulse count that is displayed is for a fairly old measurement. Therefore, a portable pulse counter to be worn on the arm for realtime display of pulse measurement or a portable electronic instrument equipped with a pulse-measurement function will not be able to display pulse changes on a realtime basis, making the unit inconvenient and posing a difficulty in comprehending the wearer's condition.
Furthermore, increasing the number of sampling points results in a larger volume of data to be sampled, increasing the time required for frequency analysis. Additionally, since the address for sampling must also be increased, these factors cause both the size and cost of the device to increase. Moreover, if the address must be increased simply for increasing the number of sampling points, it will be necessary to use a processor that may be too fast for other mechanisms that are incorporated, such as a clock mechanism, which can be a problem.
If a personal computer (PC) is used for analysis, increasing the number of sampling points also increases the amount of data to be sent to and processed by the PC, causing processing speed degradation.
Therefore, the objective of this invention is to provide a measurement device and a measurement method that can provide output values, such as pulse count and body movement pitch, at high precision without increasing the number of sampling points, and thus can output more natural values.
Another objective of the invention is to provide a measurement device and a measurement method that can process data within a short time period without extending the data fetch time or processing time by making it possible to display highly precise output values without increasing the number of sampling points, and that can output pulse count and body movement pitch on a realtime basis in a portable device or at a high speed in a processing device such as a personal computer.
Still another objective is to provide a compact and inexpensive portable electronic instrument, in which multiple functions are incorporated in addition to pulse-count and pitch measurement functions, that can produce highly precise values using a simple configuration based on the present invention.